This invention relates generally to automatic gear changing systems and in particular to a hydraulic regulating device for load shifted gears, particularly for use in automatic transmissions for motor vehicles including a source of pressure fluid, a return conduit, a high pressure conduit connected to the source, a manually operable hydraulic selector valve for preselecting a gear stage, a working pressure conduit connected via the selector valve to the high pressure conduit, and a plurality of shift control valves assigned to respective coupling elements.
In a known hydraulic regulating device of this kind each coupling element for respective gears in the automatic transmission is provided with a damping member which ensures that the pressure in the coupling is built up according to a time function. In this manner it is attained that couplings which during the changing of the speed of the gear stage has been immediately connected to a pressure conduit by means of the assigned directional control valve, are not activated suddenly but with a gradually increasing coupling force. As a result, a soft and generally shock-free gear shift of the automatic transmission is obtained when changing the gears. At the same time a pressure dependent on the engine load is applied to the coupling dampers in order to vary the coupling force according to the load to be transmitted.
The coupling dampers have a stable characteristic line which of course due to the mass production of the dampers exhibits considerable tolerances. Since the aforementioned load dependent pressure is superposed to the time dependent damping behavior of the coupling dampers in order to achieve the aforedescribed shock-free engagement of the couplings, an exact adjustment and accurate trimming of the coupling dampers is absolutely necessary. Because in the mass production considerably large tolerance deviations may occur, it is necessary in many cases that the coupling dampers be selected according to the limits of their damping characteristic lines. In addition, the prior art coupling dampers enable the soft activation or engagement of the couplings but do not enable a controlled release or disengagement of the couplings in their connecting or sliding operation. In order to disengage the couplings the latter are directly released via directional control valves. Consequently, the pressure decrease occurs in sudden jerks and so does the coupling disengagement relation. In shifting the automatic transmission to a lower gear stage, considerable jerks are therefore unavoidable.